Manufacture of electric cables

ABSTRACT

In the manufacture of an electric cable, a layer of wires is applied to an advancing core by a method comprising drawing the wires through a fixed lay plate, at least two intermediate lay plates and a final lay plate, and then bringing them into engagement with the core. The final lay plate is caused to oscillate about the core through an angle greater than 720* , each half-cycle of its oscillation comprising a major part during which the angular velocity of the lay plate has a substantially uniform value and a minor part during which its angular velocity is greater than that uniform value. The intermediate lay plates are caused or permitted to oscillate at the same frequency as and in phase with the final lay plate, the amplitude of each oscillating lay plate exceeding that of the preceeding lay plate by less than 360*. In the resulting layer each of the wires extends about the core in a helical path which reverses its circumferential direction at intervals spaced apart along the length of the core by a distance which is at least twice the length of lay of the wires about the core.

United States Patent [72] Inventor Eric Lyons St. l-lelens, England [21] App1.No. 772,106

[22] Filed Oct. 31, 1968 [45] Patented Mar. 23, 1971 [73] Assignee British Insulated Callenders Cables Limited London, England [32] Priority Nov. 1, 1967 [3 3] Great Britain [5 4] MANUFACTURE OF ELECTRIC CABLES 10 Claims, 5 Drawing Figs.

[52] US. Cl. 57/3, 57/ 34, 5 7/59 [51] Int.Cl B6511 81/08 [50] Field of Search 57/3, 6, 10-15, 34, 59, 34 (AT) [56] References Cited UNITED STATES PATENTS 2,813,392 11/1957 Woosey 57/15X 3,187,495 6/1965 Christian et al. 57/34 3,408,807 1 1/1968 Sylthe 57/59 3,460,334 8/1969 Lawrenson 57/10 Primary Examiner-John Petrakes A!torney-Webb, Burden, Robinson and Webb ABSTRACT: In the manufacture of an electric cable, a layer of wires is applied to an advancing core by a method comprising drawing the wires through a fixed lay plate, at least two intermediate lay plates and a final lay plate, and then bringing them into engagement with the core. The final lay plate is caused to oscillate about the core through an angle greater than 720, each half-cycle of its oscillation comprising a major part during which the angular velocity of the lay plate has a substantially uniform value and a minor part during which its angular velocity is greater than that uniform value. The intermediate lay plates are caused or permitted to oscillate at the same frequency as and in phase with the final lay plate, the amplitude of each oscillating lay plate exceeding that of the preceeding lay plate by less than 360. In the resulting layer each of the wires extends about the core in a helical path which reverses its circumferential direction at intervals spaced apart along the length of the core by a distance which is at least twice the length of lay of the wires about the core.

1 MANUFACTURE OF ELECTRIC CABLES This invention relates to electric cables and their manufacture. More particularly it is concerned with electric cables which consist of or comprise a layer of wires each of which extends about a center core in a helical path which periodically reverses its circumferential direction. When used in this specification the term wire means a single wire, whether bare or insulated; or a group of two or more wires, whether bare or separately or collectively insulated, for example a twisted telephone pair of a quad. The term core when used in this specification means a single wire either bare or insulated, or a group of wires associated in any manner, which may or may not be enclosed within a common envelope.

More particularly, the' invention relates to the manufacture of cables comprising a layer of wires each extending around a core in a helical path which periodically reverses its circumferential direction by passing the wires from their supply bobbins to and through a fixed lay plate and to and through a lay plate oscillating angularly about the core, and then bringing them into engagement with the core, for example by means of a closing die, and to cables made by this method.

The method in accordance with the present invention comprises drawing the wires through afixed lay plate, through at least 'two intermediate angularly oscillatorily mounted lay plates and through a final lay plate which is caused to oscillate about the core through an angle greater than 720, and then bringing them into engagement withthe core to form a layer of wires which extend aboutthe core in a helical path which reverses its circumferential direction at intervals spaced apart along the length of the core by a distance which is at least twice the length of lay of the wires about the core.

The number of angularly oscillatorily mounted lay plates required between the fixed lay plate and the final'oscillating lay plate will depend to a large extent upon the angle of oscillation of the lattersince the maximum angle of oscillation of each oscillating lay plate relative to the last preceding lay plate, whether it be a fixed lay plate or an oscillating lay plate, must be less than 360 if rubbing of the wires on the core or one another at a point between-these two lay plates is to be avoided. The extent to which this maximum angle of oscillation must be less than 360 will depend to a large extent upon the diameter of the core around which the wires are to be laid;

the larger this diameter the lower the maximum permissible angle of oscillation of any lay plate relative to the preceding lay plate, for any selected lay plate diameter.

This will be more readily understood if one first considers the simple case of a single oscillating lay plate used in conjunction with a fixed lay plate of the same effective diameter. The oscillating lay plate may be arranged to oscillate to an equal extent in each direction from a neutral position in which the wires pass from the fixed lay plate to the oscillating lay plate in a direction having no circumferential component. Rotation of the oscillating lay plate through 180 from the neutral position in one direction will bring the wires together at a place midway between the two lay plates and on the centerline of the apparatus where the core is to pass. Rotation in the reverse direction through 360 will first separate the wires and the bring them together again in the same place.

If one interpolates an oscillatorily mounted lay plate of the 'same effective diameter intermediate the fixed lay plate and the oscillating lay plate the latter may, in the absence of a core, be oscillated through 360 relative to the intermediate plate without the wires becoming locked together at a place midway between the oscillating lay plate and the intermediate lay plate, and'the intermediate lay plate may be oscillated (or allowed to oscillate) through 360 relative to the fixed lay plate without the wires becoming locked together at a place midway between the intermediate lay plate and the fixed lay plate, thus permitting the oscillating lay plate next to the closing die to oscillate through 720 relative to the fixed lay plate. When a core is present, these angles will be reduced to an extent dependent upon the thickness of the core.

If more than one oscillatorily mounted lay plate is interpolated between the fixed lay plate and the oscillating lay plate next the closing die, the angle of oscillation of the final lay plate may be increased beyond 720 in order to obtain an oscillation of 720 or more at the point of application of the wires to the core whilst the angle of relative oscillation of any two successive lay plates may be reduced to accommodate the core.

To obtain an ideal lay pattern comprising accurately helical segments between abrupt lay reversals, it would be necessary for the final lay plate to change instantaneously from a uniform angular velocity in one direction to a uniform angular velocity in the reverse direction. It will be appreciated that this pattern of oscillation cannot be obtained and in accordance with an important feature of the invention the final lay plate is oscillated in a succession of half-cycles, each half-cycle comprising a major part during which the. angular velocity has a substantially uniform value and a minor part during which the angular velocity is greater than that uniform value. The minor part of the half-cycle preferably precedes the major part, and the uniform value of angular velocity is preferably the same, apart from its direction, for all half-cycles. When final lay plate is driven in this way, a substantially more abrupt reversal of lay is obtained than when the angular velocity is always equal to or below a predetermined uniform value. Such a drive can be obtained by using a reversible hydraulic motor regulated by an electronically controlled valve. Reversal may be initiated by limit switches geared to the final lay plate.

The oscillatorily mounted layplates interpolated between the fixed lay plate and the final oscillating lay plate may be free running and oscillate in response to torque exerted by the wires passing through them. However, we prefer, especially where several lay plates are interpolated, to drive them through appropriate angles in order to reduce the tensile loading of the wires and friction between them and the lay plate dies through which they pass. The appropriate angle in terms of the actual angle of oscillation of the final oscillating lay plate through which an interpolated lay plate should be driven will depend upon the number of interpolated lay plates and its position in the series. The lay plate next to the fixed lay plate will be oscillated through the smallest angle and that next to the final lay plate will be oscillated through the greatest. In general where there are m interpolated oscillatorily mounted lay plates, the angle through which the nth lay plate should be driven is preferably n/(m l of the angle of oscillation of the final lay plate. However it is not essential that the angle of oscillation of each lay plate relative to the last preceding lay plate should be 360 or some specific angle less than 360. The relative angles of oscillation may differ from one another to some extent in which case the actual angle of oscillation of any interpolated lay plate will differ from that calculated by the above formula.

Where the intermediate lay plates are positively driven, it is convenient to mount the moveable parts of the limit switches on the first intermediate lay plate since it oscillates through an angle of less than 360. This has the advantage over the use of separate gearing that the inertia of the oscillating system is not appreciably increased. Preferably the spacing of the interpolated lay plates from one another is the same and equal to the spacing of the first of them from the fixed lay plate and to that of the last of them from the final lay plate.

As the actual angle through which each interpolated lay plate oscillates differs from that through which each other lay plate oscillates each must, if driven, be driven at a speed appropriate to its actual angle of oscillation. This may be effected by providing outside the paths of the wires, a ring of teeth on each interpolated lay plate and on that of the final lay plate and driving each by means of a toothed belt or idle pinion from a pinion on a common play shaft, the pinions being of various diameters. For example, if the relative angle of oscillation is 300 in each case and if there are two interpolated lay plates, the actual angles of oscillation of the intepolated lay plates will be 300 in the case of the interpolated lay plate next to the fixed lay plate, 600 in the case of the second interpolated lay plate and 900 in the case of the lay plate next to the closing die. These may be driven by toothed belt drives from pinions mounted on a common lay shaft and having p, 2p and 3p teeth respectively.

The axial spacing of the lay plates should preferably be at least equal to and preferably several times greater than the pitch diameter of the rings of dies in the lay plates so that at any lay plate the angle between the line of approach and line of departure of any wire shall not be excessive when the angular deviation of that lay plate from the neutral position is a maximum. I

It will generally be most convenient to thread up the machine when the intermediate and final oscillatible lay plates are in the neutral position, that is, when each lay plate is midway between its two extreme positions. In this neutral position, the wires are threaded so that each passes from the fixed lay plate to the final lay plate without any circumferential component of travel. If threading up is done when the lay plates are in any other position particular care must be taken to ensure that each wire takes a path which is appropriate having regard to the varying position of the oscillating lay plates relative to the fixed lay plate. Threading up under such conditions is facilitated by appropriately numbering the wire dies in each lay plate.

It is preferably for the wire dies or guides in each lay plate, to be of some material having a low coefficient of friction with the surface of the wire, e.g. with copper, aluminum polythene or p.v.c. They may be of porcelain or polytetrafiuoroethylene. It may also in some cases be advantageous to spray the wires before and during their passage through the array of lay plates with a lubricant that is compatible with any wire insulation (or other material used in the manufacture of the cable) with which it comes into contact.

The invention will be more fully described, by way of example, with reference to the accompanying drawing wherein:

FIG. 1 is a diagrammatic perspective view of cable-making apparatus illustrating the basic principles of the invention;

FIG. 2 is a cross section through a practical form of assembly for the first intermediate lay plate of the apparatus of FIG. 1;

FIG. 3 is an end view of the assembly of FIG. 2;

FIG. 4 is a diagram of a preferred drive mechanism and control arrangement; and

FIG. 5 is a graph showing the required form of oscillation of the final plates of the apparatus shown in FIG. 1.

In the example shown in FIG. 1, the method and apparatus in accordance with the invention is used in the manufacture of a cable comprising four wires 1-4 extending about a central core 5. Each wire passes through corresponding apertures in a number of similar lay plates 6-9 before being applied to the core and secured by a flexible binder 10, which may be a textile cord, applied in an open helix by lapping head 11. Lay plate 6 is stationary, and the supply reels 12, 13 for the core and the wires respectively and the takeup reel 14 for the cable produced revolve only about their own axes. The final lay plate 9 and intermediate lay plates 7, 8 oscillate angularly about the axis of the core 5 and are shown close to their respective positions of maximum displacement in an anticlockwise direction as seen from the takeup end of the apparatus. The displacement of the first intermediate lay plate 7 is limited to about 150 in each direction from the angular position of the fixed lay plate, which allows sufficient clearance for a central core having a diameter up to about one-half of the distance r of the wire aperture in the die-plates from the center of the plate (2rsin l5=0.5 1 7r if the thickness of the wires is negligible). The second intermediate lay plate 8 oscillates at the same frequency as an in phase with lay plate 7, and its maximum displacement is l50 from the instantaneous position of lay plate 7, or 300 from the position of the fixed lay plate 6. Similarly, the final lay plate 9 oscillates in phase with the other oscillating lay plates with a maximum displacement of 150 from the instantaneous position of lay plate 8, or 450 from the position of the fixed lay plate 6. Thus the amplitude of the oscillation of the final lay plate is 900 i.e. two and one-half full turns. The interval between reversals of lay on the cable will be somewhat less than this, but an interval of about 2.1 turns can readily be obtained. For the manufacture of cables having a larger interval between reversals further intennediate lay plates may be inserted, provided that friction effects do not lead to excessive tension in the wires.

Application of the wires to the core may be controlled solely by the flexible binder 10 as shown in the drawing, or a closing die may be used. In the latter case a securing cord may be applied, if necessary, either downstream of the die or in the mouth of the die.

The oscillating lay plates are preferably driven by belts 15- -17 from a layshaft 18, the driving wheels 19-21 having diameters in the ratio 1:2:3. To avoid slipping at reversals, toothed wheels and belts are preferred. The layshaft itself is driven by reversible means 22.

A practical form of the oscillating lay plate 7 is shown in FIGS. 2 and 3, together with certain associated parts of the apparatus. The lay plate 7 is an aluminum alloy disc having a central aperture 23 for the core and a number of apertures 24 for the wires. The latter have linings 25 of polytetrafluoroethylene to reduce friction on the wire. Several sets of wire apertures may be provided for use in making different forms of cable. The lay plate is mounted on a tubular rotor 26, also of aluminum alloy, carried in bearings 27 on the frame 28 of the machine. The rotor bears a toothed wheel 29 for engagement with the toothed belt 15. The lay plate carries a permanent magnet 30 to operate limit switches 31, 32 which initiate reversal of the drive as the lay plate approaches the limit of its displacement in each direction.

The other oscillating lay plate assemblies may be identical with that described, except that the magnet and limit switches are not required.

The apparatus 22 (FIG. 1) for driving the lay shaft 18, which distributes power to the lay plates is preferably of the form indicated schematically in FIG. 4. A reversible hydraulic motor 33 which drives the lay shaft 18 through reduction gearing 34 is powered by a pump 35 and regulated by a spool valve 36 controlled by solenoid 37. The current supplied to the solenoid by the electronic controller 38 is reversed on operation of the limit switches 31, 32 to give successive signals A, B and its magnitude is controlled in response to a signal from tachogenerator 39 indicating the actual speed of the motor and a signal C representing the desired speed. The signal C may be preset, but preferably it is derived from the drive mechanism which advances the core.

The required oscillation characteristic of the final lay plate is shown in FIG. 5 which is a plot of angular velocity against time. Each half-cycle comprises a major part X where the angular velocity is uniform, preceded by a minor part Y where the angular velocity is higher than in the major part. Reversals initiated at A and B are as rapid as practicable, but the commencement of reversal is fairly gradual. This characteristic can be obtained by using a second-order control system in which the controller 38 is a conventional type of closed loop feedback amplifier in which the component values have been so selected that the system is slightly underdamped. Procedures for the design of such an amplifier, including the provision of predetermined damping characteristics, are well known and are analyzed for example in the text books Automatic Feedback Control System Synthesis" by John G. Truxall (McGraw-l-Iill 1955) and Principles of Automatic Control" by Martin Healey (English Universities Press I967). There is a tendency for the lay-angle in adjacent parts of the cable to become equalized, with the result that the reversal zones become lengthened; by providing a zone of enlarged lay angle in the part Y of each half-cycle, this lengthening is substantially reduced, with consequent improvement in electrical properties.

Where the intermediate lay plates aredriven independently of the final lay plate, their oscillation. characteristics may differ from that of the final lay plate, since only the latter affects the form of the cable produced.

I claim: 1. in the manufacture of an electric cable, the method of applying a layer of wires to an advancing core which comprises:

A. drawing the wires:

i. through a fixed lay plate; i

ii. through at least two intermediate angularly oscillatorily mounted lay plates; and

iii. through a final lay plate which is caused to oscillate about the core through an angle greater than 720, each half-cycle of the oscillation comprising a major part during which the angular velocity of the lay plate has a substantially uniform value and a minor part during which its angular velocity is greater than that uniform value; and then B. bringing the wires into engagement with the core to form a layer of wires which extend about the core in a helical path which reverses its circumferential direction at intervals spaced apart along the. length of the core by a distance which is at least twice the length of lay of the wires about the core. 2. A method as claimed in claim 1 inwhich the said minor part of each half-cycle precedes the major part thereof.

3. A method as claimed in claim 1 in which the said uniform value of the angular velocity is the same, apart from its direction, for all half-cycles.

4. A method as claimed in claim] comprising driving the said intermediate lay plates to oscillate at the same frequency as and in phase with the final lay plate, the amplitude of oscillation of each oscillating lay plate exceeding that of the preceding lay plate by less than 360.

5. A method as claimed in claim 1' comprising bringing the wires into engagement with the core under the control of a flexible binder which is being helically applied to the core and which also serves to secure the wires to-the core.

6. Apparatus for applying a layer of wires to a core in the manufacture of an electric cable comprising:

A. a fixed lay plate, at least two intermediate angularly oscillatorily mounted lay plates and a final lay plate;

B. means for oscillating the final lay plate about the core through an angle greater than 720 in a succession of halfcycles, each half-cycle comprising a major part during which the angular velocity of the final lay plate has a substantially uniform value and a minor part during which the angular velocity is greater than that uniform value; and

C. means for passing the wires successively through the fixed, intermediate and final lay plates and then bringing them into engagement with the core to form a layer of wires which extend about the core in a helical path which reverses its circumferential direction at intervals spaced apart along the length of the core by a distance which is at least twice the length of lay of the wires about the core.

7. Apparatus as claimed in claim 6, further comprising means for oscillating each intermediate lay plate at the same frequency as and in phase with the final lay plate, the amplitude of oscillation of each oscillating lay plate, including the final lay plate, exceeding that of the preceding lay plate by less than 360.

8. Apparatus as claim in claim 7 wherein the said means for oscillating the final lay plate and the said means for oscillating the intennediate lay plate comprise a single reversible hydraulic motor regulated by an electronically controlled valve and limit switches mounted with their movable parts on the first intermediate lay plate which initiate operation of the valve to reverse the motor,

9. Apparatus as claim in claim 6 wherein the said means for oscillating the final lay plate comprises a reversible hydraulic motor regulated by an electronically controlled valve and limit switches geared to the final lay plate which initiate operation of the valve to reverse the motor.

10. Apparatus as claimed in claim 6 wherein the said means 'forbringing the wires into engagement with the core comprises a lapping head arranged to apply a flexible binder to the core over the layer of wires after it has passed through the final lay plate. 

1. In the manufacture of an electric cable, the method of applying a layer of wires to an advancing core which comprises: A. drawing the wires: i. through a fixed lay plate; ii. through at least two intermediate angularly oscillatorily mounted lay plates; and iii. through a final lay plate which is caused to oscillate about the core through an angle greater than 720*, each halfcycle of the oscillAtion comprising a major part during which the angular velocity of the lay plate has a substantially uniform value and a minor part during which its angular velocity is greater than that uniform value; and then B. bringing the wires into engagement with the core to form a layer of wires which extend about the core in a helical path which reverses its circumferential direction at intervals spaced apart along the length of the core by a distance which is at least twice the length of lay of the wires about the core.
 2. A method as claimed in claim 1 in which the said minor part of each half-cycle precedes the major part thereof.
 3. A method as claimed in claim 1 in which the said uniform value of the angular velocity is the same, apart from its direction, for all half-cycles.
 4. A method as claimed in claim 1 comprising driving the said intermediate lay plates to oscillate at the same frequency as and in phase with the final lay plate, the amplitude of oscillation of each oscillating lay plate exceeding that of the preceding lay plate by less than 360*.
 5. A method as claimed in claim 1 comprising bringing the wires into engagement with the core under the control of a flexible binder which is being helically applied to the core and which also serves to secure the wires to the core.
 6. Apparatus for applying a layer of wires to a core in the manufacture of an electric cable comprising: A. a fixed lay plate, at least two intermediate angularly oscillatorily mounted lay plates and a final lay plate; B. means for oscillating the final lay plate about the core through an angle greater than 720* in a succession of half-cycles, each half-cycle comprising a major part during which the angular velocity of the final lay plate has a substantially uniform value and a minor part during which the angular velocity is greater than that uniform value; and C. means for passing the wires successively through the fixed, intermediate and final lay plates and then bringing them into engagement with the core to form a layer of wires which extend about the core in a helical path which reverses its circumferential direction at intervals spaced apart along the length of the core by a distance which is at least twice the length of lay of the wires about the core.
 7. Apparatus as claimed in claim 6, further comprising means for oscillating each intermediate lay plate at the same frequency as and in phase with the final lay plate, the amplitude of oscillation of each oscillating lay plate, including the final lay plate, exceeding that of the preceding lay plate by less than 360*.
 8. Apparatus as claim in claim 7 wherein the said means for oscillating the final lay plate and the said means for oscillating the intermediate lay plate comprise a single reversible hydraulic motor regulated by an electronically controlled valve and limit switches mounted with their movable parts on the first intermediate lay plate which initiate operation of the valve to reverse the motor.
 9. Apparatus as claim in claim 6 wherein the said means for oscillating the final lay plate comprises a reversible hydraulic motor regulated by an electronically controlled valve and limit switches geared to the final lay plate which initiate operation of the valve to reverse the motor.
 10. Apparatus as claimed in claim 6 wherein the said means for bringing the wires into engagement with the core comprises a lapping head arranged to apply a flexible binder to the core over the layer of wires after it has passed through the final lay plate. 